1. Field of the Invention
The present invention relates to a vehicle brake system with a hydraulic brake device and a regenerative brake device and more particularly to a brake control system which is adapted to cooperatively control the hydraulic brake force generated by the hydraulic brake device and the regenerative brake force generated by the regenerative brake device.
2. Discussion of the Related Art
Recently, in a hybrid vehicle equipped with an engine and a generator-motor as plural driving sources for driving the hybrid vehicle, it became a common practice that the vehicle stores the electricity by converting the kinetic energy into the electric energy as a regenerative energy by means of the generator-motor upon braking operation thereby to improve fuel efficiency. In this meaning, the generator-motor is considered to be the regenerative brake device which applies regenerative brake force to the drive wheels of the vehicle. Since the regenerative brake device cannot generate sufficient brake force by alone, normally the hydraulic brake device, which is operated to generate brake force by means of hydraulic pressure, is used in combination therewith. Accordingly, it has become necessary to control the vehicle brake system by cooperatively using both the hydraulic brake force generated by the hydraulic brake device and the regenerative brake force generated by the regenerative brake device. For this reason, various cooperative control technologies have been proposed and one of such technologies is shown in a Japanese unexamined published patent application (publication No. 2006-312384, hereafter as Patent Document 1).
The Patent Document 1 discloses a vehicle regenerative brake and friction brake device which includes a regenerative brake means (regenerative brake device) and a regenerative brake torque control means, a friction brake means (hydraulic brake device) and a friction brake torque control means and a total brake torque determining means, wherein the regenerative brake torque and the friction brake torque can be cooperatively controlled upon braking operation. Further, the vehicle regenerative brake and the friction brake device includes an estimating means for estimating an estimated value of the regenerative brake torque, considering the delay of the actual value relative to a command value of the regenerative brake torque (regenerative brake force), wherein the friction brake torque control means controls the friction brake torque based on the total brake torque and the estimated value of the regenerative brake torque. According to this structure, the friction brake torque is highly accurately controlled so that the delay of actual value relative to the command value of the regenerative brake torque is compensated thereby to prevent uncomfortable brake operation feeling to an operator of the vehicle.
It should be noted here that in a brake system for a hybrid vehicle including the one in the Patent Document 1, it is general to structure the control portion of the hydraulic brake device and the control portion of the regenerative brake device (in other words, generator-motor) by different electronic control devices to each other and to functionally connect the two through a telecommunication means. For this reason, the technology disclosed in the Patent Document 1 achieved the effects that possible ill-affects derived from the delay of actual value relative to the command value of the regenerative brake force (torque) can be minimized, in other words, the ill-affect derived from the communication time delay until the command value reaches the generator-motor and the ill-affect resulted from responding time of the generator-motor can be minimized. However, since the communication transferring the command value of regenerative brake force (regeneration request brake value) and the actual value (regenerative execution brake value) is made with constant time intervals, the communication delay until the actual value returns becomes also a problem. For example, the control portion of the hydraulic brake device cannot immediately recognize the actual value due to the communication delay, even under the generator-motor being generating the regenerative brake force in response to an indicated value through the communication means. Accordingly, the control portion of the hydraulic brake device continues to indicate generation of the controlled hydraulic brake force until the control portion recognizes the actual value, presuming that the regenerative brake force has not yet been generated. Under this situation, since the regenerative brake force has been actually generated and the controlled hydraulic brake force has been continued to be applied, overlapping with the regenerative brake force, an excessive brake force was applied that may lead to deteriorate the brake feeling of the operator of the vehicle. In addition, the overlapping of the controlled hydraulic brake force reduces generation of the regenerative brake force that may lead to inefficient regeneration operation.
Further, the technology disclosed in the Patent Document 1 shows the method for obtaining an estimate value of the regenerative brake force. Since the regenerative brake device is subject to a vehicle operational condition, such as for example, vehicle running condition, the amount of re-generable brake force (brake force that can be regenerated) may vary, depending on the vehicle condition. Therefore, the operation of the regenerative brake device is not necessarily performed according to the estimated value. It is therefore, preferable to cooperatively control both hydraulic brake device and regenerative brake device, knowing the value of re-generable brake force in the regenerative brake device.
The invention is made considering the issues of the above related arts and it is an object of the invention to provide a vehicle brake system which can exhibit high regeneration efficiency as well as improve brake operation feeling of an operator of the vehicle by controlling brakes, knowing the re-generable brake force by the regenerative brake device.